One piece molds

[Nina]

I am making one piece molds of bowls that I carve into and then bisque fire. I am having a hard time keeping the bowl from floating up, when pouring in the plaster, any suggestions?

[Chris Campbell]

It's difficult to picture your problem ... I don't grasp how the bowl could float if you were filling it with plaster or putting plaster over it.

Do you have images?

[lynny]

I am making one piece molds of bowls that I carve into and then bisque fire. I am having a hard time keeping the bowl from floating up, when pouring in the plaster, any suggestions?

 

Do you have the bowls upside down within the cottle walls? If so a thing coil of clay around the rim will hold it in place or make a 1" 'slab' the exact shape of the bowl rim for it to rest on the you have a 'negative' area of the slip version to trim back.

[BeckyH]

One piece molds are best made with the object upside down, stuck to the table with a coil of damp clay. You can also make a collar of clay that runs around the rim and works as a reservoir for extra slip during the casting process. You then trim the edge once the piece is stiff.

[missholly]

i pour plaster into my cottle board walls and push the bowl bottom down into the plaster up to the rim.

you only need to hold it there for a few minutes until it holds itself.

[Marcia Selsor]

Yes, cast it upside down after you securely attach your model to something like a piece of plexiglass. set up you cottle frame pieces. You could secure with clay or hot glue.

Use a mold release on the bowl.Mix the plaster, spray the surface with diluted alcohol to remove surface air bubbles. Slowly pour the plaster and tap when fininshed to get all the air bubbles to rise to the surface.

marcia

[Lucille Oka]

I am making one piece molds of bowls that I carve into and then bisque fire. I am having a hard time keeping the bowl from floating up, when pouring in the plaster, any suggestions?

 

 

 

You are making a slump bowl mold? Hump molds could not possibly float. If you are making a one piece slip cast mold for a bowl this will be a difficult slip casting method. You need to employ a ‘spare’ to help remove the excess slip and hold the cast in place until set; thus requiring at least two pieces.

 

But if you want to just continue with what you are doing I would suggest a partial plaster pour to embed the model in a bed of plaster. Place your soaped ‘model’ bowl upside down in your cottle box and pour about an inch of plaster all around the rim of your model. Just before the plaster sets rough up the surface a bit, and then let the plaster set. After the plaster has cooled, wet it down a bit then proceed to pour the rest of the plaster on top of the previous pour, covering your model.

 

This is just a way to stop the floating but it is not the proper way to make a bowl mold for slip casting.

 

 

 

 

[Nina]

Thank you for all of your helpful answers! Nina

[KellyRainey]

I am making one piece molds of bowls that I carve into and then bisque fire. I am having a hard time keeping the bowl from floating up, when pouring in the plaster, any suggestions?

 

 

I have seen some artists put tape over the top of it and then stick the tape to the sides of the cottle/box, etc. You could try that as well. I am told it works well.

Note - There are instructions somewhere online (cannot remember where I saw them) for making large round bottom bowls with balloons by pouring the plaster in the cottle/box, etc then quickly stuffing the balloon down into the plaster and then taping the balloon down.